The present invention relates to a CRT panel glass for use in a color-television tube.
An envelope of a CRT comprises a panel portion for projecting video images, a tubular neck portion with an electron gun arranged therein, and a flare-shaped funnel portion connecting the panel portion and the neck portion. Electron beams emitted from the electron gun excite phosphors arranged on an inner surface of the panel portion to emit light so that the video images are projected on the panel portion. At this time, X-rays bremsstrahlung are produced inside the tube. If the X rays bremsstrahlung leak out of the tube through the envelope, an adverse influence is given to the human body Therefore, the envelope of the type is required to have a high X-ray absorbability.
In order to improve an X-ray absorption coefficient of a glass, PbO may be contained in the glass. However, if the glass containing PbO is used for a panel glass, coloring called browning will occur due to irradiation of the electron beams and X-rays which are produced upon projecting the video images. This results in a problem that the images can not be seen clearly.
Therefore, in order to suppress the browning, development is made of a CRT panel which contains a large amount of SrO and BaO, instead of PbO, in the glass.
However, if the above-mentioned components are contained in the glass in a large amount, there arises a problem that devitrifying stones such as barium disilicate (BaOxc2x72SiO2) and strontium silicate (SrOxc2x7SiO2) are deposited in the glass and a liquidus temperature rises to make the formation of the glass difficult. In addition, the above-mentioned devitrifying stones may be produced on an image display surface of the panel glass to cause defects so that the production yield is decreased.
If the contents of SrO and BaO are decreased in order to suppress production of the devitrifying stones such as barium disilicate and strontium silicate, the X-ray absorption coefficient are decreased correspondingly.
Therefore, it is an object of the present invention to provide a CRT panel glass which has an X-ray absorption coefficient not smaller than 28.0 cmxe2x88x921 at 0.6 xc3x85, which can lower a deposition temperature range for barium disilicate and strontium silicate, and which can prevent production of devitrifying stones thereof.
The present inventors repeatedly carried out a variety of experiments and, as a result, found a composition range which, even if a large amount of SrO and BaO are contained in order to obtain a sufficient X-ray absorbability, is capable of suppressing the increase in liquidus temperature due to presence of the devitrifying stones resulting from the above-mentioned components and propose the present invention.
According to the present invention, there is provided a CRT panel glass which does not substantially contain PbO, which contains, in mass percent, 9-9.5% SrO and 8.5-9% BaO with SrO/(SrO+BaO) being 0.50-0.53, and which has an X-ray absorption coefficient of 28.0 cmxe2x88x921 or more at 0.6 xc3x85.
The CRT panel glass of the present invention contains a large amount of SrO and BaO and therefore has an X-ray absorption coefficient of 28.0 cmxe2x88x921 or more at a wavelength of 0.6 xc3x85 even if PbO is not contained.
Generally, in case where a large amount of SrO and BaO are contained in the glass, devitrifying stones such as barium disilicate and strontium silicate tend to be produced. This results in a rise in liquidus temperature which makes the formation of the glass difficult. In the CRT glass of the present invention, production of the above-mentioned devitrifying stones can be suppressed to lower the liquidus temperature to 860xc2x0 C. or less so that formation of the glass can be facilitated by the limitation of, in mass percent, 9-9.5% SrO and 8.5-9% BaO with SrO/(SrO+BaO) being 0.50-0.53.
According to the present invention, there is also provided a CRT panel glass which does not substantially contain PbO, which contains, in mass percent, 50-70% SiO2, 0-4% Al2O3, 0-4% MgO, 0-4% CaO, 9-9.5% SrO, 8.5-9% BaO, 0-2% ZnO, 5-10% Na2O, 5-10% K2O, 0-3% ZrO2, 0-3% TiO2, 0-2% CeO2, 0-2% Sb2O3, and 0-2% P2O5 with SrO/(SrO+BaO) being 0.50-0.53, and which has an X-ray absorption coefficient of 28.0 cmxe2x88x921 or more at 0.6 xc3x85.
Following is the reason for limiting the glass composition as mentioned above in the present invention.
PbO is a component which improves the X-ray absorbability of the glass. However, inclusion of PbO will cause coloring, which is called browning, by irradiation of electron beams and X-rays. Therefore, this component should not be introduced into the glass of this invention.
SiO2 is a component serving as a network former of the glass. However, if the content is less than 50%, the viscosity of the glass is excessively lowered so that formation becomes difficult. The content of more than 70% leads to a coefficient of thermal expansion which is excessively low and will not match the coefficient of expansion of a funnel glass. Preferably, the content of SiO2 is within the range of 53-67%.
Al2O3 is also a component serving as a network former of the glass. However, if the content is greater than 4%, the viscosity of the glass is increased so that the formation becomes difficult. Preferably, the content of Al2O3 is not greater than 3%.
MgO and CaO are components serving to facilitate melting of the glass and to adjust the coefficient of thermal expansion and the viscosity. However, if the contents are greater than 4%, the glass is easily devitrified and the liquidus temperature rises so that the formation becomes difficult. Preferably, the content of each of MgO and CaO is not greater than 2%.
SrO is a component serving to facilitate the melting of the glass, to adjust the coefficient of thermal expansion and the viscosity, and to improve the X-ray absorbability. However, if the content is greater than 9.5%, strontium silicate is produced and devitrification will easily be caused. If the content is less than 9%, barium disilicate is produced and devitrification will easily be caused, resulting in decrease in production efficiency. Preferably, the content of SrO is within the range of 9.1-9.4%.
BaO, like SrO, is also a component serving to facilitate the melting of the glass, to adjust the coefficient of thermal expansion and the viscosity, and to improve the X-ray absorbability. However, if the content is more than 9%, barium disilicate is produced and devitrification will easily be caused. If the content is less than 8.5%, strontium silicate is produced and devitrification will easily be caused, resulting in decrease in production efficiency. Preferably, the content of BaO is within the range of 8.6-8.9%.
ZnO, like SrO and BaO, is a component serving to facilitate the melting of the glass, to adjust the coefficient of thermal expansion and the viscosity, and to improve the X-ray absorbability. However, if the content is more than 2%, the glass is easily devitrified and the liquidus temperature rises so that the formation becomes difficult. Preferably, the content of ZnO is not greater than 1%.
Na2O and K2O are components to adjust the coefficient of thermal expansion and the viscosity. However if the contents are more than 10%, the viscosity is excessively low so that the formation becomes difficult and the electrical resistivity is degraded. If the contents are less than 5% , the coefficient of thermal expansion is excessively low and will not match the coefficient of expansion of the funnel glass. Preferably, the content of each of Na2O and K2O within the range of 6-9%.
ZrO2 is a component to adjust the coefficient of thermal expansion and the viscosity and to improve the X-ray absorability. If the content is greater than 3%, wadcite (K2O.ZrO2.3SiO2) is deposited and the formation becomes difficult. Preferably, the content of ZrO2is within the range of 0.1-2.5%.
TiO2 is a component to suppress UV solarization of the glass. If the content is greater than 3%, the effect can not remarkably be improved and the material cost becomes high. Preferably the content of TiO2 is within the range of 0.1-2%.
CeO2 is a component to suppress X-ray browning of the glass. If the content is greater than 3%, the glass will be colored and the sufficient optical transmittance can not be obtained. Preferably, the content of CeO2 is within the range of 0.1-2%.
Sb2O3 can be used as a fining agent. However, if the content is greater than 2%, the effect can not be remarkably be improved and the material cost becomes high. Preferably, the content of Sb2O3 is 1% or less.
P2O5 can be added to suppress the tendency of devitrification. However, if the content is greater than 2%, separation of a liquid phase occurs and, inversely, devitrification will easily be caused. Preferably, the content of P2O5 is 1% or less.
In order to suppress the deposition of barium disilicate and strontium silicte and to lower the liquids temperature, ther ration of SrO/(SrO+BaO) should be limited to 0.50-0.53. If the ratio is smaller than 0.50, barium disilicate is remarkably deposited so that the liquidus temperature dramatically rises. Furthermore, if the ratio is greater than 0.53, strontium silicate is remarkably deposited so that the liquidus temperature dramatically rises.
Besides the above-mentioned composition, a coloring agent such as CoO, NiO, and Fe2O3 may be added up to 0.3% in order to adjust the transmittance.